Forging tool

ABSTRACT

A forging tool for precision forging of components of intermetallic or high-temperature stable phases with high yield stresses and shapeable at temperatures up to 1400° C. is made of graphite with a low-melting metal or a low-melting metal alloy infiltrated into its open-pored cavities, where metal carbides are created by heat treatment and form with the graphite a two-phase material hardened by subsequent quenching. The tool features high strength thanks to the yield stress increasing as the temperature increases at forging temperatures up to 1400° C., and is oxidation-resistant. It is electrically conductive, and has a low heat capacity, so that rapid inductive heating of the tool involving only low energy expenditure, short forging cycles and an inexpensive isothermic shaping process are possible. It has good lubrication properties, low wear and low manufacturing costs.

This application claims priority to German Patent Application DE102010045698.5 filed Sep. 16, 2010, the entirety of which is incorporated by reference herein.

This invention relates to a forging tool, in particular for hot die forging of components of intermetallic or high-temperature stable phases with high yield stresses.

In hot forging at high die temperatures up to 1150° C., metallic die materials such as molybdenum, nickel or high-temperature resistant steels are usually used. For example, die materials having a nickel basis, such as Inconel 718, are used for forging temperatures up to 900° C., while for forging temperatures up to 1150° C., molybdenum alloys are used as the die material. Forging tools of this type are disadvantageous to the extent that they are, due to high material and manufacturing costs, on the one hand very expensive and on the other hand become soft at high forging temperatures and hence are unsuitable for precision forging. The metallic forging tools furthermore have a high heat storage capacity, meaning a high heat retention, so that the heating-up process requires much time and involves heavy expenditure of energy. For forging temperatures above 1150° C., these materials lack the required strength, so that dies made from them cannot be used for forging of intermetallic or other high-temperature stable phases such as titanium aluminide, which can only be shaped at temperatures above 1250° C.

The forging tools that can be used in this temperature range above 1150° C. are made of special fiber-reinforced ceramic materials such as CSiC. The main disadvantages of forging tools made of ceramic materials are their low wear resistance, the breaking out of the material in edge areas of the die and the non-existent possibility, due to the lack of electrical conductivity, of inductive heating of the die, which is advantageous for the forging process. Furthermore, the known metallic die materials tend towards heavy oxidation at high temperatures.

The present invention, in a broad aspect, provides a forging tool which can be heated up quickly and easily, is temperature-stable and wear-resistant also in the temperature range necessary for precision forging of intermetallic compounds, and can furthermore be manufactured at low cost.

It is a particular object of the present invention to provide solution to the above problems by a forging tool designed in accordance with the features described herein.

Advantageous embodiments of the present invention will become apparent from the present description.

The underlying idea of the invention is to design the forging dies in graphite with a low-melting metal or a low-melting metal alloy infiltrated into its open-pored cavities, where metal carbides are created by the heat treatment and form with the graphite a two-phase material hardened by subsequent quenching. The forging tool thus designed features high strength, thanks to the yield stress increasing as the temperature increases at forging temperatures up to 1400° C., and at the same time is oxidation-resistant, and can be used at these forging temperatures for precision forging of components made of intermetallic compounds, such as titanium aluminides. In addition to its electrical conductivity, the forging tool in accordance with the present invention also has a low heat capacity, so that rapid heating of the tool involving only low energy expenditure, short forging cycles and an inexpensive isothermic shaping process is possible. The new tool is furthermore distinguished by good lubrication properties, low wear and low manufacturing costs.

In a further embodiment of the invention, the low-melting metals infiltrated into the graphite are of aluminum or aluminum alloys. The heat treatment for the formation of the aluminum carbides is effected at temperatures above 400° C., where the two-phase material includes differing aluminum carbides depending on the heat treatment.

In another embodiment of the invention, the low-melting metals can also be magnesium or magnesium alloys.

The present invention is more fully described in the following exemplary embodiment.

Turbine blades made of titanium aluminide for a gas-turbine engine are manufactured by precision die forging at a temperature above 1250° C. The forging tool, including an upper die and a lower die with engraving integrally formed into them, is made of a graphite material infiltrated with molten aluminum which was heat-treated after the infiltration of the aluminum into an open-pored graphite block at a temperature above 400° C. Due to the reaction of the aluminum with the graphite, aluminum carbides are formed which lead to a substantial improvement of the strength properties of the graphite and in particular prevent its oxidation, where in this material combination, the good lubrication properties of the graphite and the characteristic feature of the graphite that the yield stress increases as the temperature increases, which is important for a forging tool, can be exploited. With dies made of aluminum-infiltrated graphite, turbine blades made of titanium aluminide, in accordance with the present exemplary embodiment, can be forged at the high forging temperatures of up to 1400° C. required for this material without damaging the dies. Thanks to its good conductivity and the low heat capacity of the die material, the forging tool can be heated up inductively and also very quickly, such that the energy expenditure is low and short forging cycles are possible.

The invention is not limited to the present exemplary embodiment. The proposed forging tool can also be used for other components made of other shapeable materials. Instead of aluminum or aluminum alloys, other low-melting metals or metal alloys, such as magnesium, can be used as the infiltration material, which after infiltration into the graphite and appropriate heat treatment, form a two-phase material of graphite and metal carbides stable at temperatures up to 1400° C. and quickly heatable by induction, the material being suitable in particular for manufacturing forging tools for the precision forging of components including intermetallic compounds. 

What is claimed is:
 1. A forging tool, comprising: a body of open-pored graphite and low-melting metals or metal alloys infiltrated into the open-pored graphite to form a two-phase material; the two-phase material having been heat treated to create metal carbides and hardened by quenching, the material being electrically conductive at low heat capacity, having high strength at forging temperatures up to 1400° C. and being oxidation-resistant.
 2. The forging tool of claim 1, wherein the low-melting metals or metal alloys infiltrated into the graphite are selected from a group consisting of aluminum and aluminum alloys, and the tool has been heat treated for formation of the aluminum carbides at temperatures above 400° C., with a type of aluminum carbide being present depending on the heat treatment.
 3. The forging tool of claim 2, wherein the tool is inductively heatable.
 4. The forging tool of claim 3, wherein the tool is useable for isothermic forging at forging temperatures up to 1400° C.
 5. The forging tool of claim 1, wherein the low-melting metals or metal alloys are selected from a group consisting of magnesium and magnesium alloys.
 6. The forging tool of claim 5, wherein the tool is inductively heatable.
 7. The forging tool of claim 6, wherein the tool is useable for isothermic forging at forging temperatures up to 1400° C.
 8. The forging tool of claim 1, wherein the tool is inductively heatable.
 9. The forging tool of claim 8, wherein the tool is useable for isothermic forging at forging temperatures up to 1400° C.
 10. The forging tool of claim 1, wherein the tool is useable for isothermic forging at forging temperatures up to 1400° C.
 11. A method of making a forging tool, comprising: forming a body of open-pored graphite; infiltrating low-melting metals or metal alloys into the open-pored graphite to form a two-phase material; heat treating the two-phase material to create metal carbides; hardening the material by quenching; thereby forming a material that is electrically conductive at low heat capacity, has high strength at forging temperatures up to 1400° C. and is oxidation-resistant.
 12. The method of claim 11, and further comprising: selecting the low-melting metals or metal alloys infiltrated into the graphite from a group consisting of aluminum or aluminum alloys; heat treating the tool at temperatures above 400° C. to form the aluminum carbides, with a type of aluminum carbide being present depending on the heat treatment.
 13. The method of claim 12, wherein the tool is inductively heatable.
 14. The method of claim 13, and further comprising using the tool for isothermic forging at forging temperatures up to 1400° C.
 15. The method of claim 11, and further comprising selecting the low-melting metals or metal alloys from a group consisting of magnesium or magnesium alloys.
 16. The method of claim 15, wherein the tool is inductively heatable.
 17. The method of claim 16, and further comprising using the tool for isothermic forging at forging temperatures up to 1400° C.
 18. The method of claim 11, wherein the tool is inductively heatable.
 19. The method of claim 18, and further comprising using the tool for isothermic forging at forging temperatures up to 1400° C.
 20. The method of claim 11, and further comprising using the tool for isothermic forging at forging temperatures up to 1400° C. 